Lighting or lighting engineering deals with the rational use of light sources in order to allow good vision. Lighting is the result of illuminating through the use of luminous fluxes, natural (mediated by architectural elements) or emitted by artificial sources (generally electrical equipment) in order to obtain certain levels of light (illuminance) on the object (in the broad sense) to be illuminated. The related technique is called lighting engineering. Further purposes of lighting are also to create scenic effects, accent and with its generating equipment (lamps) to make furniture. The term lighting is also used as a simplification and with the meaning of “lighting system”.
The problem of lighting has different aspects depending on whether it is necessary to illuminate closed environments (indoor lighting) or open spaces (outdoor lighting). Interior lighting can be natural or artificial. Natural lighting uses daylight that penetrates into the environment to be illuminated through windows or more generally through appropriate glass surfaces (skylights, sheds, etc.). This lighting depends essentially on sky conditions and season and is therefore highly variable both during the day and during the year. Lighting requirements therefore imply constraints in the design of buildings, whose orientation must be such as to allow good use of daylight.
To characterize the natural lighting conditions of an environment, the daylight factor is introduced, which is defined as the ratio between the average illuminance of the room, excluding direct sunlight (illuminance that also depends on the reflective properties of the walls, therefore essentially on their color), and the illuminance that would be outdoors with the same sky. It is clear that natural lighting, given its characteristics, must be supplemented or replaced by artificial lighting. Artificial lighting was first obtained by means of fires, oil lamps, flashlights, candles, then by means of oil, gas and acetylene lamps. With the spread of electricity, these systems were replaced by electric lamps; non-electric light sources still in common use are portable oil or liquid gas lamps, used in campsites and generally in areas not served by a distribution network of electricity.
Artificial lighting is called direct if the luminous flux produced by one or more sources directly invests the illuminated objects, and the rate reflected by walls, ceilings, screens, etc. is less than 10%; indirect if the luminous flux invests the illuminated objects after being reflected for a rate greater than 90%. The use of computer software and hardware is increasingly widespread in the field of lighting with the intention of reproducing real luminous atmospheres, with the possibility of modulating the infinite variations of light and colors at will. There are integrated devices able to program and remote control the illumination levels of light sources, consisting of both a single light point and complex systems of luminaires, according to the activities carried out in the individual areas of the plant. For each light point it is possible to choose and program the most suitable level of luminous intensity, which can be modified as desired by each individual user.
Then there are intermediate cases between these types of lighting. The choice of a particular type of lighting is linked to general criteria aimed at achieving conditions of visual well-being: therefore, both abrupt transitions from strongly lit areas to areas with weak lighting (luminance contrasts) and glare caused by intense, unshielded sources or by narrow, highly reflective areas must be avoided. One of the main data for the design of lighting systems is the value of illuminance that you want to obtain, which depends on the needs of the activity that takes place in the illuminated areas.
Types of lighting
- Direct light: provides the best illuminance for the work surface because the light beam is projected directly onto it without any artificial reflection. It involves, however, a high contrast between the dark and light parts and needs, therefore, a background light so that the eye does not become fatigued.
- Indirect light: the light beam reaches the point to be illuminated only after a reflection, on a wall or ceiling for example. With the background light obtained in this way, the overall illumination is soft and softer than that of the direct type and is free of shadows. It has a higher cost than the previous one and needs, of course, relatively bright walls and additional points of light to obtain good illumination.
- Semi-direct light: is a mixed type of lighting, with characteristics of direct and indirect types. Like indirect light, it needs bright walls but is also suitable for neutral-toned walls and ceilings. A percentage of the light beam strikes directly on the plane of the illuminated objects.
- Shadowless light: is produced by a strong beam of light that significantly reduces shadows.
- Scialitic light: produced by a particular lamp, a form of very intense lighting used in particular in operating rooms during surgery. It is practically shadowless because it uses various beams of light aimed at the work surface from multiple directions.
Lighting engineering is the technical-scientific discipline that deals with the illumination of spaces and environments, both indoor and outdoor, using both sunlight and artificial light. To produce an artificial lighting project the knowledge of lighting engineering is a necessary but not sufficient condition, since a lighting project is based on interdisciplinary knowledge, such as:
- Physiology and psychology of vision: light perception of the human eye, lighting ergonomics, visual comfort
- Architecture and design: choice of suitable light for interiors or exteriors, buildings, monuments, squares, gardens, museums
- Electrotechnics: use of electricity in lighting, types of lamps, plant engineering
- Regulation: safety (emergency lighting), energy saving, light pollution
Lighting engineering is the part of Technical Physics that studies the problems of both natural and artificial lighting in order to ensure conditions of environmental well-being and visual comfort for humans.
Regarding the nature of light and its mode of transmission, already in 1670 Christian Huygens, Dutch astronomer and physicist, developed a wave theory of light in opposition to the corpuscular theory of Newton, with which the phenomena of polarization and interference were finally explained. He also advanced the hypothesis that the color of light was a function of wavelength. However, only in 1862, after the experiments on the speed of light conducted by French Foucault, the controversy of the two theories was finally dissolved in favor of Huygens’ wave hypothesis.
It was Maxwell’s turn, on the basis of Faraday’s studies, to unify, in 1873, concepts and experimental data until then collected, with the publication of his “Treatise on Electricity and Magnetism”, that showed how light was nothing else than electromagnetic waves of small wavelength, that could be transmitted, therefore, without the need of any medium (the famous “ether” mentioned by Huygens). Maxwell’s theory found final confirmation in the experimental work conducted by German Hertz in 1887. Finally it must be remembered that in 1905 Einstein, on the basis of Planck’s work, postulated that even the transmission of energy of a beam of light was done by “packets” (quanta) called photons. The quantum theory allowed to understand phenomena not interpretable in the light of the only wave theory, such as, for example, photoelectricity.
An integral and preliminary part of lighting engineering is Photometry, which deals with the measurement of the amount of radiant energy emitted by a source, or received from a surface, in relation to the sensations produced in the individual through the eye. Modern photometry is relatively recent, dating back to the eighteenth century, the first who formulated the concepts that still today are the basis were Bouguer and Lambert. In particular Bouguer’s work Essai d’Optique was published in 1729, while Lambert’s work on photometry appeared in 1760. From these early works it emerged that the eye has the property of being influenced not by the amount of ray energy that strikes it, but by the relationship between this and time, that is the power of the beam of incident radiation.
Modern lighting technology can be placed at the beginning of the nineteenth century; in fact, the first electrically powered artificial source is probably the one that Davy, an English researcher, created in 1813. This innovative source could not have been created if Alessandro Volta had not invented his famous battery at the beginning of 1800. The real development of modern lighting technology took place first in 1850 with the introduction of the first permanent magnet current-generating machines. of permanent magnet current and later in 1875 with the introduction of alternating current generators. The first artistic lighting systems date back, in fact, to 1879 (the Duomo in Milan and the Colosseum in Rome).
The eye also has the ability to attribute to light a quality (color), which depends on the wavelength of radiation. The fundamental problem of photometry is therefore to measure the sensations produced by beams of radiation different, not only as power, but also as wavelength. In particular, the chromatic aspect of radiation is, because of its importance, the object of specific study in colorimetry.
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